The present invention relates generally to exhaust after treatment systems (EATS) and, more particularly, to methods and equipment for monitoring components in an EATS.
Government regulations impose strict limits for diesel engine exhaust with regard to, among other things, particulate and NOX emissions. Compliance with these regulations requires a multi-component EATS. A typical EATS will include a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction catalyst system (SCR), as well as an AHI (Advanced Hydrocarbon Injection) nozzle (also known as a “seventh injector”) for injecting fuel upstream of the DOC to facilitate heating of the EATS and regeneration of the DPF.
To ensure proper functioning of the DOC, it is known to monitor temperature downstream of the DOC and upstream of the DPF to diagnose a malfunctioning DOGC. If temperature is lower than expected, that may indicate a malfunctioning DOC. However, other problems with the EATS may also be the cause for lower than expected temperatures downstream of the DOC. For example, a clogged AHI nozzle will also result in temperatures downstream of the DOC and upstream of the DPF being lower than expected. Also, the method can not monitor the catalytic activity of a catalyzed DPF, which is also critical for controlling NMHC emissions and providing appropriate NO2/NOx ratio to a downstream SCR for optimal SCR NOx conversion efficiency. While it is possible to determine that the AHI nozzle is clogged by use of a flow meter in the AHI line, this solution adds substantial cost and complexity to the EATS and its control system. While it is also possible to use the SCR NOx conversion efficiency to provide some information about the feeding gas composition from an upstream DPF, there are a few other factors which can lead to lower than normal SCR NOx conversion efficiency other than feeding gas compositions, for example diesel emission fluid (DEF) dilution, degradation of SCR catalyst itself, clogged or leaking DEF loop, etc. A SCR can also be not sensitive to feeding gas compositions while the residence time of exhaust time is long or its inside temperature is high.
It is desirable to provide a method for monitoring several components of an EATS at once without adding substantially to the cost or complexity of the EATS or its control system.
According to an aspect of the present invention, a method is provided for monitoring components in an exhaust after treatment system (EATS) for a diesel engine, the EATS comprising, in order from upstream to downstream, an AHI nozzle, a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction catalyst sytem (SCR). The method comprises measuring heat released (QDOC) across the DOC during an AHI injection event, measuring heat release from AHI fuel (QEATS) across the DOC and the DPF during the AHI injection event, measuring NOX conversion efficiency (ηSCR) from NOX to N2 across the SCR while AHI is not in use, calculating heat input from AHI fuel (QAHI) during performance of the AHI injection event with a fully functioning AHI nozzle, calculating a DOC HC Slip Factor=1−(QDOC/QEATS), calculating an AHI Flow Loss Factor=1−(QEATS/QAHI), and identifying a malfunctioning AHI nozzle, DOC, DPF, or SCR by comparing each of calculated DOC HC Slip Factor, calculated AHI Flow Loss Factor, and measured NOX conversion efficiency with desired values.
According to another aspect of the present invention, an exhaust after treatment system (EATS) for a diesel engine is provided. The EATS comprises an AHI nozzle, a diesel oxidation catalyst (DOC) downstream from the AHI nozzle, a first temperature sensor upstream of the DOC, a diesel particulate filter (DPF) downstream of the DOC, a second temperature sensor downstream of the DOC and upstream of the DPF, a selective catalytic reduction catalyst system (SCR) downstream of the DPF, a third temperature sensor downstream of the DPF and upstream of the SCR, a first NOX sensor upstream of the SCR, a second NOX sensor downstream of the SCR, and a controller. The controller is arranged to determine heat released (QDOC) across the DOC during an AHI injection event based on a first temperature measurement signal and a second temperature measurement signal from the first temperature sensor and the second temperature sensor, respectively, determine heat released (QEATS) across the DOC and the DPF during the AHI injection event based on the first temperature measurement signal and a third temperature measurement signal from the first temperature sensor and the third temperature sensor, respectively, determine NOX conversion efficiency (ηSCR) from NOX to N2 across the SCR while AHI is not in use based on NOX measurement signals from the first and second NOX sensors, calculate heat input from AHI fuel (QAHI) during performance of the AHI injection event with a fully functioning AHI nozzle, calculate a DOC HC Slip Factor=1−(QDOC/QEATS), calculate an AHI Flow Loss Factor=1−(QEATS/QAHI), and identify a malfunctioning AHI nozzle, DOC, DPF, or SCR by comparing each of calculated DOC HC Slip Factor, calculated AHI Flow Loss Factor, and measured NOX conversion efficiency with desired values.
According to yet another aspect of the present invention, a controller is provided for an exhaust after treatment system (EATS) for a diesel engine, the EATS comprising an AHI nozzle, a diesel oxidation catalyst (DOC) downstream from the AHI nozzle, a first temperature sensor upstream of the DOC, a diesel particulate filter (DPF) downstream of the DOC, a second temperature sensor downstream of the DOC and upstream of the DPF, a selective catalytic reduction catalyst system (SCR) downstream of the DPF, a third temperature sensor downstream of the DPF and upstream of the SCR, a first NOX sensor upstream of the SCR, and a second NOX sensor downstream of the SCR. The controller is arranged to determine heat released (QDOC) across the DOC during an AHI injection event based on a first temperature measurement signal and a second temperature measurement signal from the first temperature sensor and the second temperature sensor, respectively, determine heat released (QEATS) across the DOC and the DPF during the AHI injection event based on the first temperature measurement signal and a third temperature measurement signal from the first temperature sensor and the third temperature sensor, respectively, determine NOX conversion efficiency (ηSCR) from NOX to N2 across the SCR while AHI is not in use based on NOX measurement signals from the first and second NOX sensors, calculate heat input from AHI fuel (QAHI) during performance of the AHI injection event with a fully functioning AHI nozzle, calculate a DOC HC Slip Factor=1−(QDOC/QEATS), calculate an AHI Flow Loss Factor=1−(QEATS/QAHI), and identify a malfunctioning AHI nozzle, DOC, DPF, or SCR by comparing each of calculated DOC HC Slip Factor, calculated AHI Flow Loss Factor, and measured NOX conversion efficiency with desired values.